Full contact seals, such as lip seals, are widely known in rotating assemblies for joining mutually rotatable parts together in order to render the assembly substantially impervious or at least to reduce the flow of fluids or the passage of particles from one side of a seal to the other side of the seal to protect the system from damages caused by such fluids or particles.
In specific wind turbine applications, sealing between a stator, such as the nacelle, and a rotor, such as the hub, is an important issue for preventing the damage of the inner parts of the nacelle. In particular, in wind turbine applications it is important to prevent external agents from entering the nacelle through the gap between the hub and the nacelle as well as to prevent inside pressurized air leakage. In particular offshore applications, it is important to prevent external air and water from entering the nacelle.
In this respect, such full contact seals require well-machined friction surfaces in order to ensure a good surface contact for an efficient sealing. For this reason, full contact seals are not desirable in wind turbine applications in which large diameter parts are involved. In addition, high wear undergone by these types of seals result in undesirable weakening, particularly in the case of elastomeric seals such as rubber seals. Replacement of large seals is difficult, if at all possible, and very costly in wind turbine applications and specifically in offshore environments.
In order to overcome the problem of sealing in wind turbine applications, brush type seals have been proposed in the prior art. Brush seals have been proven to be a good solution for wind turbine applications involving large tolerances and surfaces having non-uniformities.
In this respect, document EP2306009 describes a seal arrangement intended to avoid grease leakage in wind turbine applications. This arrangement comprises two mutually rotatable parts and a brush type seal. The brush type seal is carried by one of the parts for sealing both parts when they are moved relative to each other.
Although this approach could be efficient, it does not however deal with the problem of ingress of external agents into the wind turbine such as external air and water and other elements that are present, especially in offshore or marine applications.
Labyrinth type seals have also used in wind turbine prior art applications. One example of this is disclosed in US2008246224. The seal arrangement disclosed in this document comprises a labyrinth seal arrangement intended to minimize bearing lubricant leakage in a radial direction. The labyrinth seal is arranged perpendicular to the axis of rotation of the rotor and includes a plurality of rings arranged concentrically in concentric grooves. This arrangement requires the use of a pumping gasket to prevent flow in the axial direction.
The problem with this kind of labyrinth seals in wind turbine applications where large sized parts are involved is that their manufacturing is capital intensive. Large pieces in wind turbine applications together with the vibrations produced when the wind turbine is in service render the use of labyrinth seals ineffective for the sealing of mutually rotatable parts, especially for air or pressurized air sealing.
In U.S. Pat. No. 6,010,132 the use of a labyrinth type seal with a brush type seal in a flow path between two relatively moving parts is combined. The labyrinth seal is formed by a plurality of teeth extending radially from one part toward the other part. The brush seal includes a plurality of bristles extending generally radially between said teeth.
Although this solution could be particularly useful in gas turbines that work under high inner pressures and temperatures, this is directed to systems in which the gap to be sealed with the brush, that is, the gap between the teeth, is reduced. For this reason, this construction is not effective for wind turbine applications where inner pressures are reduced and where large tolerances are involved due to the large size of the rotary parts.
Therefore, a need still remains for a sealing arrangement capable of ensuring an effective sealing between two mutually rotatable parts in wind turbine applications.